Juan Carlos Gutierrez, Lopez's attorney, said his client was charged with arson and conspiracy, but charges of murder and terrorism were dropped, CNN reported Thursday.

Anti-government protests in Venezuela raged in several cities overnight, with the official death toll rising to six. Student-age demonstrators burned cars and tires and threw Molotov cocktails, and security forces responded by firing tear gas and rubber bullets into the crowds.

Especially violent and sustained clashes occurred in the western Andean cities of San Cristobal and Merida, Venezuelan newspaper El Nacional reported.

Wednesday's hearing to formally charge Lopez and determine whether he would be released took place in a bus parked outside the prison where he is being held, officials said, because of security concerns about the courtroom.

"It seems very unorthodox," Gutierrez told CNN.

Lopez surrendered to authorities this week before tens of thousands of supporters he had called to the streets. Some of the largest anti-government protests during President Nicolas Maduro's 11-month tenure have taken place in recent weeks.

Human rights groups warned about the danger of turning the protests over social and economic issues into a persecution of political opponents.

The charges against Lopez, who has organized protests demanding better security, an end to shortages and protected freedom of speech, "smack of a politically motivated attempt to silence dissent in the country," Amnesty International said in a statement.

Human Rights Watch also warned that Venezuela must avoid "scapegoating" political opponents.

Officials have accused the United States of plotting to destabilize the government. This week, Venezuela expelled three U.S. diplomats, accusing them of conspiring to bring down the government.

Videos of the violence in Caracas showed armed men on motorcycles riding through protester areas amid sounds of heavy gunfire, screams in the street and the banging of pots and pans by residents in apartment buildings to show their displeasure.

"The government came out to kill people, to try to shut up people with lead," opposition leader Henrique Capriles said during a news conference Thursday.

Maduro repeated his accusation that "right-wing fascists" financed by Washington were behind the violence, which he said was part of a plot to topple his socialist government.

"In Venezuela, they're applying the format of a coup d'etat," he said in a nationally broadcast speech.

Maduro alleged his foes wanted to create enough chaos to "justify a foreign military intervention."

Capriles, who lost to Hugo Chavez in the 2012 presidential elections and then to Maduro in an election 10 months ago to determine who would succeed Chavez after he died, denied a coup was taking place.

"Civilians don't launch coups," he said in remarks quoted by the Wall Street Journal, "the military does."

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